It has been long-established to utilize fermented products of microorganisms for animal feeds. Utilization of fermented products can be categorized into two types, one is utilization of substances which are produced (decomposed or synthesized) by a specific microorganism and the other is utilization of microbial activities of living cell mass of a specific microorganism.
Japanese Unexamined Patent Application Gazette No. 57(1982)-206342 discloses a composition of feedstuff for red sea-bream (Perciformes pagrus) containing fermented products of Phaffia rhodozyma belonging to yeast. The term "fermented products" in this reference means fermented culture broth microbial cell mass collected therefrom, substances obtainable by physically destroying or chemically decomposing microbial cells. Said microorganisms produce a red pigment, astaxanthin, which is effective for color development in epidermis of red sea-bream and which is accumulated inside cells, thus it is expressly described in said reference that when fermented culture the broth is used it is essential to include microbial cell mass therein.
Japanese Examined Patent Application Gazette No. 57(1982)-39153 discloses an animal feed supplement containing fermented products of Streptomyces eurocidicus variety asterocidicus belonging to the Class Actinomycetes. The terms "fermented products" in this reference mean fermented culture broth or its concentrated liquid including or excluding microbialcell mass thereof, dried materials obtainable therefrom, and wet or dried microbial cell mass collected therefrom. That is, the invention in this reference utilizes the substances which are produced by said microorganisms and which are included inside and outside microbial cells thereof.
Japanese Unexamined Patent Application Gazette No. 50(1975)-68867 discloses animal feed containing fermented products of yeast belonging to Sacchalomyces cerevisiae which products is effective for reducing serum cholesterol. The terms "fermented products" used in said reference include fermented culture broth including or excluding microbial cell mass, since the invention in this reference utilizes the substance which is produced outside microbial cells.
Japanese Unexamined Patent Application Gazette No. 56(1981)-58491 discloses an immuno-activating substance having anti-tumor function which is isolated and purified from the filtrate of incubated culture broth of microorganisms belonging to the genus Bifidobacterium. In this reference the filtrate of incubated culture broth in which a strain of microorganisms belonging to the genus Bifidobacterium is anaerobically incubated is physico-chemically fractionated to obtain effective substances having molecular weights within a certain range.
Animal feedstuff containing viable or living cell mass of lactic acid bacteria which are useful bacteria dwelling in the animal intestine and which serve initiation or conservation of favorable intestinal flora is known. For example, animal feed containing incubated culture broth including living or viable cell mass of lactic acid bacteria and supplement to be added to animal feeds consisting of powdery material dried from the incubated culture broth containing viable microbial cell mass of lactic acid bacteria have been commercially available.
In recent years, antibiotics have been widely utilized in live-stock industry. Minute amounts in the ration has proved to increase the growth of animals. Repetitive administration of antibiotics, however, entails some problems. One of the problems is undesirable influences to the human health caused by the antibiotics which can be transferred into live-stock products such as meat and eggs. Another problem is that repetitive administration may cause disturbance of normal intestinal flora and may cause in turn decline of defense against microbial infections to animals.
In order to solve the latter problem, it has been attempted to feed living or viable cell mass of useful bacteria dwelling in animal intestine for reestablishment of normal intestinal flora. However, it cannot be expected that the useful bacteria are settled and propagated in animal intestin when antibiotics are concurrently administered, since such bacteria are susceptive to antibiotics without exception.
As will be clear from the forgoings, there has not been known a composition of animal feed containing the residual liquid of incubated culture broth obtainable by substantially excluding microbial cell mass of Bifidobacteria and/or lactic acid bacteria from the incubated culture broth or solid material dried from the residual liquid.
The inventors of the present invention have discovered as the result of their effort that the residual liquid of incubated culture broth excluding microbial cell mass of Bifidobacteria and/or lactic acid bacteria has an excellent effect as a growth-promotong supplement for animal feeds. The present invention is based on this discovery.